lkml.org 
[lkml]   [2014]   [Oct]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: bisected: futex regression >= 3.14 - was - Slowdown due to threads bouncing between HT cores
From
Date
On Wed, 2014-10-08 at 13:04 -0400, Linus Torvalds wrote: 
> On Wed, Oct 8, 2014 at 11:37 AM, Mike Galbraith
> <umgwanakikbuti@gmail.com> wrote:
> >
> > 11d4616bd07f38d496bd489ed8fad1dc4d928823 is the first bad commit
> > commit 11d4616bd07f38d496bd489ed8fad1dc4d928823
> > Author: Linus Torvalds <torvalds@linux-foundation.org>
> > Date: Thu Mar 20 22:11:17 2014 -0700
> >
> > futex: revert back to the explicit waiter counting code
>
> While that revert might make things a tiny bit slower (I hated doing
> it, but the clever approach sadly didn't work on powerpc and depended
> on x86 locking semantics), I seriously doubt it's really relevant.
> It's more likely that the *real* problem itself is very
> timing-dependent, and the subtle synchronization changes here then
> expose it or hide it, rather than really fixing anything.
>
> So like Thomas, I would suspect a race condition in the futex use, and
> then the exact futex implementation details are just exposing it
> incidentally.

Whew, good, futex.c is hard. Heads up chess guys <punt>.

-Mike



\
 
 \ /
  Last update: 2014-10-08 20:41    [W:0.090 / U:0.364 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site